As infusion bags which are used in infusion treatments in medical fields, blow-molded containers obtained by blow-molding a synthetic resin such as polyethylene, polypropylene, or polyvinyl chloride, or soft bags manufactured by heat-sealing a film are used. Among these, soft bags are widely used since these are light, have a small volume at the time of disposal, and do not require an air needle that causes nosocomial infection at the time of administration. In such soft bags, polyolefin films of polyethylene or polypropylene have been used which are eluted in small amounts when wet sterilization is performed thereon under high pressure and which have good transparency and flexibility.
However, when a polyolefin film is used, there is a problem in that the soft bag production efficiency per hour is low. That is, when a bag is manufactured by heat-sealing a polyolefin film in a short period of time at a high temperature in order to increase production efficiency, the surface damage of the film is severe and the film has an excessively reduced thickness due to the high-temperature and high-pressure conditions of the heat sealing. Thus, the bag is likely to easily break or may be broken. In order to avoid such a problem, the bag manufacturing process by heat sealing using a polyolefin film should be performed carefully for a long period of time.
A method using a lamination film in which a heat-resistant resin layer and a sealant layer formed of a resin which is melted at a lower temperature than a heat-resistant resin are laminated is examined in order to make it possible to perform heat sealing in a short period of time at a high temperature. For example, Patent Document 1 discloses a multi-layer film in which an outer layer formed of a heat-resistant polyamide resin layer, an adhesive resin layer, a flexible polyolefin-based resin intermediate layer, and a blocking-resistant polyolefin-based resin inner layer are laminated in order from the outside.